Some streetcars and electric locomotives obtain their power from a wire suspended above the rails, commonly referred to as a "trolley wire". A conventional trolley wire includes two grooves extruded along its length. The purpose of the grooves is to provide positive means to grip the wire for the purpose of suspending it above the trolley track so that nothing interferes with the bottom of the wire, allowing the current collector of the streetcar to freely travel there along.
In many climates, however, such as the northeast region of the United States, sleet and ice may form on the trolley wire in sufficient quantities to impair the transfer of electrical power from the trolley wire to the streetcar or locomotive.